Earth Planets Space, Vol. 61 (No. 4), pp. 439-445, 2009
N. Balan1, H. Alleyne1, Y. Otsuka2, D. Vijaya Lekshmi3, B. G. Fejer4, and I. McCrea5
1Control and Systems Engineering, University of Sheffield,
Sheffield S1 3JD, UK
2Solar-Terrestrial Environment Laboratory, Nagoya University, Aichi 442-8507, Japan
3Department of Physics, University of Kerala, Trivandrum 695581, India
4Center for Atmospheric and Space Sciences, Utah State University, Utah 84322-0500, USA
5Rutherford Appleton Laboratory, Didcot OX11 0QX, UK
(Received September 6, 2007; Revised January 30, 2008; Accepted February 1, 2008; Online published May 14, 2009)
The paper studies the relative importance of penetrating eastward electric field (PEEF) and direct effects of equatorward neutral wind in leading to positive ionospheric storms at low-mid latitudes using observations and modeling. The observations show strong positive ionospheric storms in total electron content (TEC) and peak electron density (Nmax) at low-mid latitudes in Japan longitudes (≈125°E-145°E) during the first main phase (started at sunrise on 08 November) of a super double geomagnetic storm during 07-11 November 2004. The model results obtained using the Sheffield University Plasmashpere Ionosphere Model (SUPIM) show that the direct effects of storm-time equatorward neutral wind (that reduce poleward plasma flow and raise the ionosphere to high altitudes of reduced chemical loss) can be the main driver of positive ionospheric storms at low-mid latitudes except in Nmax around the equator. The equatorward wind without PEEF can also result in stronger positive ionospheric storms than with PEEF. Though PEEF on its own is unlikely to cause positive ionospheric storms, it can lead to positive ionospheric storms in the presence of an equatorward wind.
Key words: Ionospheric storms, electric field, neutral wind.